Marine waterjets have many advantages over other means of propelling a marine vessel, such as shallow draft, greater safety and higher efficiency. However, a disadvantage is the time-consuming process of installing the intake duct of the waterjet into the vessel hull.
An example of such a conventional marine jet drive installation is seen in FIG. 1A (labeled PRIOR ART). The traditional method of installation involves the use of overlapping and bolted bottom flange 101 and transom flange 101a around the interface between a waterjet intake duct 102 and a vessel bottom protrusion 103p in a vessel bottom 103 and a transom protrusion 104p in a transom 104. In FIG. 1B (also labeled PRIOR ART), a bottom opening 105 in bottom 103 and a transom opening 106 in transom 104 have to be laid out and cut in each vessel for each waterjet unit, making the production of the openings a labor-intensive process.
The placement procedure of the intake duct in the vessel hull is complicated and labor-intensive since the flanges of the intake duct of the waterjet have to be matched in two substantially perpendicular planes and be provided with sealer and fastener holes for attachment to protrusions 103p and 104p to produce the mechanical strength of the interface necessary to transmit the thrust and the steering and reversing forces generated by the waterjet, all while maintaining water-tight joints. Additionally, access to the bottom and transom bolts, especially in the undercut area (indicated by reference number 107 in FIG. 1A) below the lower intake duct wall, is limited and requires special tools.
It is not possible to efficiently produce a vessel with this traditional installation method of cutting, mating, sealing and bolting bottom and transom flanges with limited access in the interior of the vessel. Conventional waterjet intake ducts are made of metal, and the use of bolted mounting flanges is the common method of installing an intake duct in a vessel made of similar or dissimilar material in a new vessel or in a retro-fit installation. The cost of metallic intake ducts is high, and they are heavy and corrosion is a constant problem.
A second approach used in the production of composite hulls for waterjet applications places mold inserts in the hull mold prior to lay-up to produce the intake duct openings in the hull bottom and transom. This only avoids the layout and cutting of bottom and transom openings in the hull but still requires the labor-intensive bolted flange installation described in the paragraph above.
A third approach involves the manufacture of a composite intake duct with flanges for installation in non-composite vessel hulls and in retro-fit applications, but again, this is similarly complicated because of the complex geometries as described above.
In a fourth approach to installing an intake duct into a composite vessel hull, a waterjet intake duct plug is placed in the vessel mold as a method of producing the intake as part of the hull in the hull fabrication process. The intake duct contains an undercut in the mold shape, thus preventing release of the hull with the newly-formed intake duct. To accomplish release from the mold requires a permanent hull mold modification to allow retraction of the interfering mold parts, or, the removal and destruction of a sacrificial plug. In addition, the vessel lay-up process is considerably more complicated and time-consuming. A permanently modified hull mold precludes use of the same mold for non-waterjet hull production.
The present invention simplifies the manufacture of the intake duct, producing a flanged version for dissimilar hull material vessels or retro-fit applications and allows in-place molding of the intake duct in composite vessels. The invention solves the common problems of the four installation approaches described above. The preferred material of construction is composite to avoid the weight, corrosion and cost of metallic intake ducts. This simplification involves the manufacture of the intake duct in a manner that avoids the undercut that prevents a straight release from the mold. It is accomplished by separating the intake duct into an upper part and a lower part that each separately have no undercut so that each part can be made in a mold that permits the straight release of the part without the need for removal of a mold component that would form an undercut.
The hull bottom and transom openings are connected by the removal of the section directly between the two openings, thereby creating a common opening in the transom and hull bottom and eliminating the portion of the bottom opening and transom opening that are difficult to reach when bolting the separate bottom and transom flanges.
The upper part of the intake duct forms the upper wall with the mounting provision for the intake grid and the support of the shaft tube. It has a register to receive the lower part of the intake duct to locate it in a unique, fixed position in relation to the upper part of the intake duct. The lower part of the intake duct forms the trailing edge of the intake opening and also forms the lower wall of the intake duct. The lower part of the intake duct has a mating register to mate with the upper part. In combination, the two parts also form the surface and register for mounting the jet pump section to the discharge end of the intake duct at the transom.
In a first embodiment, the concept can be used for intake duct manufacture for applications with non-composite hulls made of metal or wood or to retro-fit existing vessels to simplify the first and second conventional approaches as described above. The flanged version of the intake duct of the present invention simplifies installation by avoiding the need for separate matching openings in the bottom and transom while also avoiding the need to place flange bolts in a difficult-to-reach location. An upper part plug is used to produce a full-thickness upper part and is provided with mounting flanges. Attachment of the lower part of the intake duct produces a complete intake duct with flanges that are continuous between bottom and transom. Hull preparation is simplified since the bottom and transom cut-outs become a common opening with one continuous seam and not two separate openings, thereby eliminating the holding of critical dimensions between transom and bottom openings. Even though the sealing and bolting processes are necessary, they are less time-consuming than a conventional installation since the bolts are all easily accessible and not hidden by undercut 107 (see FIG. 1A) of the conventional intake duct. The flange runs continuously from one side of the intake to the transom and then up and over to the other side, following the contour of the opening. The installation process for dissimilar hull materials and retro-fits is made significantly simpler.
In a second embodiment, which simplifies the third and fourth conventional approaches, a formed-in-place version of the intake duct avoids the flanged connections altogether by eliminating the flanges and molding the upper part of the intake duct directly into the hull. In this embodiment, the mold producing the upper part is now placed in the vessel mold and produces in a single lay-up process the hull with the upper part of the intake duct in place while the vessel is releasable from the mold. The lower part of the intake duct is produced in a separate mold and is inserted into the upper part of the intake duct after the hull is removed from the mold, thus forming the complete intake duct. A shaft tube is then added to complete the installation of this embodiment.
In a third embodiment of the invention, again simplifying the third and fourth conventional approaches, a shell of the upper part of the intake duct with a shaft tube in place is molded on a plug. The shell is just thick enough to maintain the shape of the upper part. The shell of the upper part of the intake duct is then mated with the fully-formed lower part thereby forming the complete intake duct shape. This combination of the shell of the upper part and the fully-formed lower part is placed in a hull mold. When the vessel is laid-up over the upper part intake duct shell with the lower part in place, the shell bonds to the lay-up and becomes a part of the hull, thus providing a completely installed waterjet intake duct upon removal of the vessel from the vessel mold. The advantage of this method is that the intake can be pre-manufactured with the shaft tube of the jet pump in place, and the mounting surface for the jet pump can be fully inspected prior to installation. Upon delivery of the intake shell to the vessel builder, it can be placed in the hull mold and, when laid-up, the intake will be an integral part of the vessel.
All embodiments of the invention provide simplified installation of a waterjet intake duct. In applications with dissimilar material (hull and intake duct) and in retro-fit applications, installation time is shortened and in a laid-up composite vessel, as part of the manufacture of the hull, very little time is added to the manufacturer's building process.